There are known disk drive devices using hard type magnetic heads. A disk drive device of this kind consists principally of at least one magnetic disk, at least one magnetic head for recording/reproducing information on/from this magnetic disk, a spindle motor for driving the rotation of the magnetic disk, an actuator drive mechanism for moving (seeking) the magnetic head in the radial direction of the magnetic disk, an auto-retract mechanism for causing the magnetic head to seek the innermost periphery of the magnetic disk at shut-off, a base plate on which each of the previously-identified components are located, and a top cover covering this base plate.
However, according to such magnetic disk drive devices, since the actuator drive mechanism and the autoretract mechanism are secured to the base plate by means of screws, it is necessary to mount these parts so as not to contact the magnetic disk. Therefore the regulation of the function and the performance of these parts was effected after the mounting thereof on the base plate. Further, in an auto-retracting mechanism including a solenoid and a lock lever operated by the solenoid, there is disposed a coil spring for energizing the lock lever and since the coil spring should be mounted in an energized state, the mounting operation is laborious and a large space for setting the coil spring is required, which was an obstacle against compacting the device. Furthermore, in a damper mechanism of an actuator, a swing arm is in contact with a rigid stopper or an elastic stopper and the stopper condition is the same on the outer periphery side, and on the inner periphery side. In the case where the rigid stopper is used, it is possible to obtain a high positional precision both on the outer and on the inner periphery side, and in the case where the elastic stopper is used, it is possible to increase the performance of the damper mechanism. However, in the present state of techniques, the stopper condition is satisfied neither on the outer periphery side nor on the inner periphery side. Further, in the magnetic head control mechanism, in order to control the movement of the magnetic head, it was necessary to make the force applied to a plate-shaped coil uniform over the movement region of the plate-shaped coil and to make the speed of the magnetic head uniform over the movement region. In addition, in a construction where an air filter was incorporated in a mold case as shown in FIG. 44, since an air filter unit 202 mounted on the mold case is fixed to the corner on a base plate 201, in the arrangement for attaching the air filter to a conventional disk drive device as shown in FIG. 44, the number of parts was great and the number of mounting steps was also great. Furthermore, since the mold case had a certain thickness, the effective area of the air filter was reduced, which decreased the purifying action. There was also a concern that the fixing positions of this mold case could loosen and that inner parts could be damaged. In addition, since a rotor 20 is directly in contact with outer wheels of bearings 14, 15 in construction of the bearing portion of an actuator in a conventional disk drive device as shown in FIG. 45, the distance between the rotor 20 and the outer wheels of bearings 14, 15 was varied due to the thermal expansion of a rotor and that the pressure fluctuated, which impaired stable rotation of the actuator. In addition, since the rotor 20 slides on the outer wheels of the bearings 14, 15 when the rotor is mounted on the bearings 14, 15, there is concern that the rotor 20 might be damaged. Furthermore, since a conventional device has no back tension adjusting piece as shown in FIG. 46, a flexible print board 101 receives a force in the direction F and by elastic force expands so that since back tension takes place on the actuator, it is necessary to set that the back tension to the actuator at 0 when the magnetic head is at the central position of the movement thereof. However the requirement should be effected at the mounting because of errors, etc. of the parts. Although it is desirable that the back tension is 0 at loading, this regulation is difficult.